The five-year warranty on the electrics on my Lexus Hybrid RX 400h ran out two years ago. The car has been well maintained by Lexus main dealers, recently had its 60,000-mile service, and has had its starter battery replaced. When are the electric motors and hybrid batteries likely to need replacing? Do I need to brace myself for some big bills? DM, London
When hybrid cars first went on sale in the UK, starting with the Toyota Prius in 2000, this was a concern raised by many. More than a decade — and 100,000 UK sales — later, it seems the hybrid components on Toyota and Lexus cars (Lexus being the luxury arm of Toyota), as well as most other hybrids, have proved pretty robust. Toyota UK says it is aware of several Prius cars using the same system as the Lexus that have clocked up more than 300,000 miles on the original motor and hybrid battery.
Figures from Toyota in America, where hybrids caught on much more quickly (more than 3m have been sold to date, 45% of which are Priuses), offer further evidence. The company quotes a battery failure rate for the first-generation Prius of about 1%; second and third-generation Priuses — launched in 2003 and 2009 respectively — fare even better, with one failure in every 40,000 cars.
If you are unlucky and your main battery fails, Lexus charges about £1,200 to supply and fit a new one. If you are still worried, you can take your car to any Toyota or Lexus dealer and for £59, or free with the next service, it will carry out a hybrid system health check. TS
I want to buy a used convertible BMW 3-series and have seen an 04-plate model for sale with only 12,000 miles on the clock. I’m attracted by the low mileage, but my friend insists that an old car that hasn’t been used much will suffer mechanical problems when it starts being subjected to more normal driving patterns. Is he right? RL, Durham
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Low-mileage cars have, generally speaking, suffered less wear and tear, but there are exceptions. The mileage may be low because the car has travelled only short distances at low speeds, never getting fully warmed up. This means unburnt fuel that leaks past the pistons gets into the oil sump and, rather than evaporating when the engine is hot, stays there. This dilutes the oil and creates a potentially harmful sludge — an emulsion of oil and the water produced as part of the combustion process.
Thinned oil does not properly protect engine parts, so wear ensues, and the sludge can cause corrosion and block the engine’s breather system.
Problems can also occur with the exhaust system: the low engine temperature allows water vapour to build up, corroding the pipes from the inside.
So if you buy any used car that has rarely been driven hard, first take it on a long, high-speed run to “blast away the cobwebs”, being careful to accelerate gently, then get the oil and oil filter changed.
Because this BMW is a convertible, it may owe its low mileage to being used for occasional long leisure trips, followed by months of not being used at all. If this is the case then your inspection checklist changes.
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Get the tyres looked at — they may need replacing because of damage caused by not having turned for a long time, or degradation by UV light if the car stays outdoors. Rubber bushes in the suspension and steering can also deteriorate, as can shock-absorber seals. So test-drive before you buy and listen for clunks and squeaks from the suspension.
The internal seals of an air-conditioning system can become impaired if the A/C is not used for long periods, needing costly repairs, so check it still works fully.
Whatever the car’s history, check that it has a record of proper maintenance. TS
When my son bought his Seat Ibiza, the garage agreed to supply a spare wheel. The size code for the car’s tyres is 215/45 R16 but the spare is a 185/65 R15, which looks much bigger and barely fits into the well. Will it be safe to use? DC, Eglwysbach, Wales
Sometimes spares don’t come in exactly the same dimensions as the other wheels — some manufacturers supply a smaller wheel with a larger tyre to save weight or cost, for example. It is important that the overall height of the spare wheel/tyre should be as close as possible to the one it replaces. Opinions vary as to how close in size the spare needs to be. Etyres (etyres.co.uk) suggests the height of the spare should be within 2.5% of the other wheels; Tyresafe (tyresafe.org) says motor manufacturers favour a limit of no more than 2% smaller or 1.5% larger.
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The first numbers in your tyre codes indicate the width of the tyre in millimetres (215 for the current tyres and 185 for the spare). The second digit (45/65) is the height of the tyre wall as a percentage of the width. The final figure is the diameter of the wheel in inches: 16in, compared with 15in for the spare.
If you work it all out, you’ll find that the height of the spare is 621mm — 3.5% larger than the other four, so it falls outside all recommendations.
Given this and the fact that the current spare barely fits in the well, we suggest that your son goes back to the seller and asks for something more suitable. DP